Charles Ellicott Commentary Numbers 12:10

"And the cloud removed from over the Tent; and, behold, Miriam was leprous, as [white as] snow: and Aaron looked upon Miriam, and, behold, she was leprous." — Numbers 12:10 (ASV)

And the cloud departed ... — The withdrawal of the cloud was the visible token of Divine displeasure. The word sar, departed, used here, is an entirely different word from the one found in Numbers 9:17: When the cloud was taken up from the tabernacle. The lifting up of the cloud was the signal for the breaking up of the camp and the resumption of the march; the withdrawal of the cloud was the token of the withdrawal of Divine presence and direction.

Leprous, white as snow. — Better, was leprous as snow, as in Exodus 4:6, where the same words are found; or, a leper (as white), as snow, as in 2 Kings 5:27. In an ordinary case of leprosy, when the disease covered the whole body and all the flesh had turned white, the man was to be pronounced clean. It was otherwise in cases where persons were smitten with leprosy by the immediate hand of God, as in the case of Moses and of Gehazi.

And Aaron looked upon Miriam ... — Or, and Aaron turned towards Miriam—i.e., he directed his attention to her, and so on. This may have been the first case in which Aaron was required to carry out the laws laid down in Leviticus 13:14, regarding the inspection of the leper; and the duties that fell to him must have been doubly painful because the leper was closely related to him, and he had been a participant in the sin that had called for such a severe punishment.